Method for transforming a gas-liquid stream in wells and device therefor

ABSTRACT

A method and device for forming a preferred gas liquid flow structure via separation of liquid and gas phases. The method and device relate to the production of gas and oil in wells. The operation and spacing of the devices ensure that the quantity of liquid moved upward exceeds the quantity of liquid running downward. The devices are sequentially installed along a tubing column. A displacement chamber in the form of an upturned cup moves axially in the tubing column. The travel of the cup is defined and controlled by a formula. The cup can have side openings in its lower section and a flange in its upper section. The flange normally blocks gas exhaust openings in a sleeve secured between the ends of the tubing members. The flange can move axially along the tubing.

CROSS REFERENCE TO RELATED APPLICATIONS

Applicants claim priority under 35 U.S.C. §119 of Russian ApplicationNo. 99123083 filed Nov. 2, 1999. Applicants also claim priority under 35U.S.C. §365 of PCT/RU00/00435 filed Nov. 1, 2000. The internationalapplication under PCT article 21(2) was not published in English.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to gas and oil production from wells and can beemployed for exploitation of oil-bearing formations on a stage ofnatural flowing of the wells and also in case of artificially supplyingof compressed air into the wells for lifting oil via air-gas liftmethod.

2. Prior Art

There are three possible structures of gas-liquid mixtures in productionwells where lifting of oil to the surface is enabled by a gas:

1. An emulsion or foam structure, which is characterized by a more orless uniform distribution of gas in liquid. The gas is present in theliquid in a form of small bubbles (smaller than diameter of the lifttubing);

2. A beaded or slugged structure. In the case of such structures most ofthe gas moves in the form of bubbles filling the whole cross-section ofa tube and alternating with slugs of liquid;

3. An axial or annular structure. In the case of such structures most ofthe gas moves along the tube axis as a continuous flow (gas blast) andthe liquid moves along the walls in the form of a thin layer.

For vertical and inclined flows one can refer to a Hewitt chart ofregimes of flowing (FIG. 1).

A method is known to form an emulsion structure of a gas-liquid flow ina lift column and devices to disperse gas into liquid (I. M. Muravievand N. N. Repin, Research of Motion of Multicomponent Mixtures in Wells,Nedra, Moscow, 1972, pp.129-139).

Its shortcomings are:

from point of view of gas consumption the emulsion structure is notoptimal;

devices to disperse gas into a liquid are mounted at the bottom end ofthe lift column where gas is injected into the liquid. However the gasbubbles coalesce while they move upward causing the flow structure to bedestroyed, i.e. it is not possible to obtain a stable structure by thismethod;

creation of emulsion structure of a gas-liquid flow (especially ifsurface active substances are added) makes more difficult the subsequentseparation of gas after the liquid (oil) has been lifted to surface.

A method is known to form a slugged regime of flowing in a gas-liquidmixture and devices therefor (Yu. V. Zaitsev et al., Theory and Practiceof Gas Lift, Nedra, Moscow, 1987, pp. 67-71). This method is the closestto the proposed one in its technical essence. In specialized literaturethis method is known as a displacement lift and is realized as follows.At the lower end of the outer row of tubes in a two pipe lift column adisplacement chamber is placed equipped with a reflux valve in whichchamber a liquid is being accumulated, and after injecting into it of agas the slug of the liquid is ejected into lift tubing and thuselevates. This process is periodically repeated. Variants ofdisplacement lift can employ compressed gas cutoff either on a surfaceor bottomhole.

The main shortcomings of this prototype are:

it is possible to create a beaded (slugged) regime of a flow at theinitial path of a lift column, but very soon it decays and becomeschaotic because the gas bubbles go into regime of floating up (drifting)and do not perform the useful work all along the whole lift column;

it is necessary to employ a two row lift column;

the devices controlling the lift are rather sophisticated;

high level of losses of compressed air;

lift production capacity by liquid is limited;

it can't be used in free flowing wells.

A device is known for periodic gas lift to elevate the liquid from wells(Authorship Certificate, USSR no 1117395, 03.02.83) that comprises atubing column and a replacement chamber comprising an overflow nipplewith a flange rigidly placed in the tubing column and a turned over cupplaced above the said nipple and forming together with the nipple achamber being in its lower part hydraulically connected with inner spaceof the tubing pipes.

This device being the most relevant by technical solution is the closestone to the proposed invention. Main shortcoming of the said known deviceis that the displacement chamber is made from rigidly connected elementsand therefore its volume available to form a gas slug is limited. Itdoes not provide a possibility of self-adjusting of a system ofgas-liquid slugs to variation of parameters of the gas-liquid mixture orhydrodynamics of a rock-well system.

SUMMARY OF THE INVENTION

Technical result of the invention is providing of a possibility ofself-adjusting of a system of gas-liquid slugs to respond variations inparameters of the gas-liquid mixture or hydrodynamics in a “rock-well”system. This technical result is achieved due to transformation of agas-liquid flow in wells due to sequential placement of devicesseparating gas and liquid phases with intervals providing conditionq_(up)>q_(down), where q_(up) is amount of liquid being elevated, andq_(down) is amount of liquid draining down. A device for transforming ofa gas-liquid flow in a well comprises a tubing column and a displacementchamber which chamber is made in a form of a turned over cup and anoverflow nipple placed in the tubing column which cup and nipple form achamber hydraulically connected in its lower part with the inner spaceof the tubing pipes, and according to this invention said cup isadmitted to move axially and its travel path is defined and regulated bythe following condition:

F>Vg(ρ_(liq)−ρ_(gas))−G−P _(stat),

where: F is a force rising the cup, V is a volume of gas in displacementchamber, G is the weight of the cup accounting for the fact that it isin liquid, P_(stat) is a hydrostatic pressure on the cup, g is agravitational acceleration, ρ_(liq) and ρ_(gas) are densities of theliquid and gas, respectively.

The technical result can be also achieved in a device wherein thedisplacement chamber is made in a form of a cup having side openings inits lower part and a flange on the top which flange normally closes thegas outlet passes in a sleeve rigidly connected at the pipe joint of thetubing column, and said flange is admitted to move axially within saidsleeve.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a Hewitt chart of regimes of flowing plotted ρ_(gas)w²_(gas) versus ρ_(liq)w² _(liq), where ρ_(liq) is density of liquid,ρ_(gas) is density of gas, w_(gas) is velocity of gas, w_(liq) isvelocity of liquid.

FIG. 2 shows a general view of a device to implement the proposedmethod. It comprises a column of tubing pipes 1, a displacement chamber2 which is made in a form of a turned over cup 3 and an overflow nipple4. To seat the device between tubes ends in the column 1 it has asetting flange 5. On an outer surface of the overflow nipple 4 thestoppers 6 are mounted to restrict the travel of the cup 3.

FIG. 3 shows another embodiment of a device to implement the proposedmethod. It comprises a column of tubing pipes 1, a displacement chamber2 which is made in a form of a cup 3 having side openings 3 a at itslower part and a flange-valve 7 on top of it which flange normallycloses the gas outlet passes in a sleeve 8, and said flange-valve 7 isadmitted to move axially in said sleeve 8.

FIG. 4 shows process of motion of a gas-liquid flow in a slugging regimein a lift column 9, where q_(up) is amount of liquid being elevated by agas slug 10, and q_(down) is amount of liquid draining down.

FIG. 5 shows a general view of a garland system of flow converters 11 ina lift column 9 where said garland system is placed above the level ofoil degassing 12. Casing pipe 13 is connected with the oil-bearing rock14 through the perforation holes.

DETAILED DESCRIPTION OF THE INVENTION

Device shown in the FIG. 2 operates as follows: a gas-liquid mixturemoving upward enters into the device through a overflow nipple 4 rigidlypositioned in a connection of pipes in column of tubing pipes 1, wheregas separates and accumulates in the turned over cup 3 while the liquidoverflows and accumulates outside the cup. Also the liquid drains downon the cup from tubes above the device. Thus both the gas and liquidslugs are formed. When volume of the gas slug in the cup 3 exceedscertain critical value, the cup starts moving up thus increasing thevolume of gas chamber. This increase of volume allows to match theregime of operation of this device with hydrodynamics of the lift columnwhich column is equipped with a garland of such devices. In a momentwhen volume and weight of drained liquid exceeds the gas pressure insidethe cup 3, the gas slug will be expelled from the cup. Once it happensthe cup will go down to seat on the flange 5 and then this process willbe repeated.

Travel pass of the cup 3 is restricted in accordance with calculation ofneeded volume of the displacement chamber 2 for each particular locationalong the lift column. Stoppers 6 which are rigidly fixed on an outersurface of the overflow nipple 4 provide this restriction.

Admittance of a free travel of the turned over cup 3 allows variation ofa gas slug volume and, once enough liquid drained on the cup, enablesfaster expelling of the gas slug into the lift column thus avoidingdiscontinuities in it what improves function of the device to form abeaded (slugged) structure of the gas-liquid flow.

Device shown in the FIG. 3 operates as follows: a gas-liquid mixturearriving from the bottom separates in the device by phases: the gasaccumulates in an annular space between the cup 3 and a column of tubingpipes 1 and the liquid remains at lower level. Also the liquid drainsdown in the cup 3 from tubes above and then flows out through openings3a in it downward. Once volume of gas in the annular space reaches acertain critical value the cup 3 will start moving up resulting inadmitting a gas slug to eject. After gas slug is released the cup havinga flange-valve 7 on top will seat back on the sleeve 8 and then thisprocess will be repeated.

Let's consider the motion of a gas-liquid flow in the beaded regimealong the lift column 9 (FIG. 4). The gas slug 10 is not a tight plug,so when it moves some liquid it pushes up (q_(up)) drains down along thepipe wall (q_(down)). When these two quantities equalize, i.e.q_(up)=q_(down), the gas slug (bubble) will transfer to the regime ofdrifting (floating) up and no longer will perform any useful work. Inthat point the next such device shall be placed entrapping the gasbubbles, compressing them into a gas slug and ejecting it to performwork to lift the liquid.

Thus a compulsive forming of a beaded (slugged) structure of an upwardflow of a gas-liquid mixture along a lift column 9 is provided.

FIG. 5 illustrates that such a process can be organized via a garlandsystem of the flow converters 11, which is built into a lift column 9and placed above the level of oil degassing 12. The number of thedevices and layout of their placing along the column can be determineddue to evaluations based on the above said conditions of theiroperation.

An oil well which flows an axial structure of the gas-liquid flow ismost inefficient due to high losses of gas per unit volume of fluidproduced from the well. The common practice of using of a surface orbottomhole flow bean doesn't significantly effect the structure of theflow and it just changes boundary conditions resulting in creation of acounter pressure on a rock thus suppressing oil production but still notavoiding gas release.

Equipping a flowing well with a system of slugging devices allows, asthe filed tests show, a reduction of oil gas exhausts into atmosphere by1.5-2 times minimum and increase oil production by 30-50% withoutessentially changing the parameters of the process.

Testing of a system of slugging devices in gas-lift wells shows thatefficiency of lifting was increased by 2-3 times.

Additional advantages provided due to equipping the flowing and gas liftoil wells with said system of slugging devices are as follows:

in contrast to the standard lift column with open lower end where theinternal hydrostatic pressure is fully applied to a bottom hole (rock),in wells with lift column equipped with the system of slugging devicesthe hydrostatic pressure is distributed along the column. It providesmore favorable conditions for oil inflowing at equal diameter of asurface bean. In gas-lift wells it makes it easier for the starting liftto operate;

system of slugging devices splits a lift column into sections thuspreventing liquid to drain to the hole bottom and therefore thusincreasing the efficiency of liquid lifting;

system of slugging devices operating to form a beaded structure ofupward flow produces pressure pulsations in the lift column which isfavorable to stimulate oil inflow from the rock;

separation of phases taking place in a system of slugging devices (incontrast to their mixing in emulsified flow) makes degassing processesin gas separators (traps) easier and faster;

system of slugging devices allows to reduce down to minimal values thelosses of gas due to beaded structure of a gas-liquid flow comparingones at axial or emulsion flow structures.

To enable current measurements to monitor wells and rocks it isadvisable to leave one of the wells of an oil field non-equipped withthe system of slugging devices as an observational one.

Strategic effect due to equipping of all flowing wells of an oil fieldwith systems of slugging devices will result in extending of duration ofa period of wells flowing by 1-2 years comparing the projected onedepending on gas-oil ratio, degree of depletion of the deposit byreservoir elastic energy, reservoir oil volume, geological specifics ofthe deposit.

Additionally one can expect the increasing of cumulative oil recovery ofoil deposits by about 10% comparing the projected values.

What is claimed is:
 1. A method for transforming liquid-gas flowstructure in a well, the method comprising: lifting a liquid phase witha gas phase; and placing a plurality of devices for separating theliquid and gas phases along a lift column, wherein said plurality ofdevices are sequentially disposed along said lift column at intervals soas to provide a condition wherein q_(up)>q_(down), where q_(up) is anamount of liquid being elevated and q_(down) is an amount of liquiddraining down.
 2. A device for transforming liquid-gas flow structure ina well, the device comprising: a tubing column; and a displacementchamber disposed within said tubing column wherein a lower portion ofsaid displacement chamber is hydraulically coupled with said tubingcolumn, and wherein said displacement chamber comprises: an overflownipple; and an overturned cup capable of moving axially within saidtubing column and having a travel path defined by a conditionF>Vg(ρ_(liq)−ρ_(gas))−G−P _(stat), where F is a force lifting saidoverturned cup, V is a volume of gas in said displacement chamber, G isa weight of said overturned cup in a liquid, P_(stat) is a hydrostaticpressure acting on said overturned cup, g is a gravitationalacceleration, and ρ_(liq) and ρ_(gas) are a density of the liquid andthe gas, respectively.
 3. A device for transforming liquid-gas flowstructure in a well, the device comprising: a tubing column; a sleeverigidly connected within said tubing column; a displacement chambermovably disposed within said tubing column, wherein said displacementchamber comprises: a cup having side openings disposed in a lowerportion of said cup; and a flange disposed on an upper portion of saidcup, wherein said flange is capable of moving axially within said sleeveand wherein said flange normally closes a gas outlet formed by saidsleeve.